The influence of several forms of vasodilation on oxygen transport will be investigated in this research project. It is known that vasodilation leads to increased vascular conductance and usually increased capillary density. Both these vascular alterations should enhance the supply of oxygen to tissues. It has been found by other investigators that this is not always the case. The purpose of this research is to examine the issue from the viewpoint of microcirculatory adjustments in the vasculature and in oxygen exchange. The microcirculation in the hamster cheek pouch and cremaster will be studied. Photographs of the microvasculature will be made to obtain information on vessel diameter, length and branching pattern during control and vasodilated states. Red cell velocity will be determined with a video densitometer; and tissue PO2 will be monitored with polarographic oxygen microelectrodes. Vasodilation will be induced by pharmacological agents, carbon dioxide and stimulation of striated muscle. These measurements will be analyzed in terms of standard mass transport models and an attempt will be made to relate microcirculatory observations to microcirculatory findings.